(a) Field of the Invention
This invention relates to bands and the like, more particularly to bands utilized for head bands for headphones, bands for wrist watches, bands for sphygmometers, bands for personal ornaments (such as hair bands and bracelets), bands for collars of dogs and cats, bands for belts of trousers, bands for tire chains and the like, and also relates to headphones having connecting bands.
(b) Description of Related Art
Conventional head bands known generally for headphones and the like are mostly kept in the form of horseshoe even when not in use as well as in use and have defects that they are bulky to carry and house, are inconvenient to carry and require housing spaces and their housing cases must be large.
The bands for wrist watches and the like are made generally of such flexible materials as metallic chains and plate-shaped plastics, require such locking members as fasteners and clips in being fitted and such locking members must be operated in fitting and removing the bands much to trouble.
Therefore, a headphone set (hereinafter simply referred to as "a headphone") having a band made easy to fit and remove and compact to house by solving such defects is mentioned in Japanese Utility Model Application No. 74970/1983 of a different inventor filed on May 19, 1983 published on Dec. 3, 1984, as SHO No. 59-180587 (hence, not prior art hereto) and assigned to the same assignee with the present application. This is formed as shown in FIG. 1 and its head band is formed of a top band 11 and side bands 10 which are extendable and contractible on both sides of this top band 11. The side band 10 is made by connecting many flat plate beam portions 12 in series in the form of a belt in the lengthwise direction, integrally bridging the flat plate beam portions adjacent to each other with a hinge 14 expanding to be in the form of V between them. Each side band 10 has a self-returning property so as to be wound inside so that the side pressure of a headphone unit 16 as fitted may be obtained by utilizing the resiliency of the hinge portions 14 when the side band 10 is expanded and the resiliency of the entire side band 10 generated in case the entire side band 10 flexes as if it were one beam when the hinge portions 14 are completely closed. When housed, as shown in FIG. 2, the side band 10 may be automatically spirally wound with the headphone unit 16 as a winding center.
However, there has been the disadvantage that, because the hinge portion 14 is V-shaped, a large force will be required to expand the side band 10 and the fitting and removing operations will not be made smoothly. Further, there has been another disadvantage that, when the side band 10 is expanded and wound, the folding part 14a of the hinge portion 14 will be locally flexed by the folding action, will be fatigued, will be reduced in the fitting force and winding action by the long use and will finally crack to be unable to use.
More particularly, when the head band is expanded, the fitting force F (the reaction Q on the side pressure) when the headphone is fitted around a head will act on the head band and this reaction Q will act as a bending moment M on the head band. The value of this bending moment will be different depending on the positions of the above mentioned many hinges. That is to say, a bending moment M corresponding to [Reaction Q].times.[Distance (arm length) r between the hinge portion and reaction Q] will act on each hinge. In other words, when the headphone is fitted, the larger the distance of the hinge portion from the headphone unit 16, the larger the bending moment acting on the hinge portion. Thereby, if the thickness of each hinge portion 14 is the same as in the headphone shown in FIGS. 1 and 2 that is, if the second moment of inertia I in the above mentioned expanding direction is the same, the larger the distance of the hinge portion from the headphone unit 16, the larger the normal stress acting on the hinge portion and the stress. Therefore, the larger the distance of the hinge portion from the headphone unit 16, the more likely to occur the permanent strain and the loss of the winding returning property.
The hinge portion 14 is required to be able to be expanded with a small operating force when the head band is to be expanded and to have a self-returning property in order to realize an automatic winding operation when the head band is to be housed.
Particularly, when the flexing operation of the hinge portion 14 when the head band is to be expanded is considered from the aspect of the stress .delta.-strain .epsilon. characteristics, if the difference between the working normal stress caused by the expanding force or fitting force F of the head band and the allowable normal stress of the hinge portion 14 of the head band is small, the stress acting on the hinge portion 14 may exceed the elastic limit and thereby the permanent set will be likely to be caused. Under such condition, the automatic winding function of the head band will be impaired and the fittabilty of the headphone will reduce. From such viewpoint, in the V-shaped hinge portion, the difference between the normal stress (the stress produced while the hinge portion 14 reaches the stated in FIG. 1 from the state in FIG. 2) caused by the expanding force or fitting force F of the head band and acting in the usual using condition and the allowable normal stress (yield point) is so small that, when the head band is repeatedly expanded and wound by the long use, the permanent set of the hinge portion 14 has been likely to occur. Such problem has occurred not only in case such formation is applied to head bands for headphones but also in case it is applied to bands for wrist watches and other bands.